Erbium doped fiber amplifiers (EDFAs) are a critical component of dense wavelength division multiplexed (DWDM) optical telecommunication systems. EDFAs amplify simultaneously applied optical signals that have different optical wavelengths within the operating wavelength range of the DWDM system. As trends to expand the channel capacity of DWDM systems increase the operating wavelength range of the systems, the performance limitations of the EDFAs are exploited and become more determinative of the performance of the DWDM systems in which the EDFAs are used. As a result, monitoring and designing modern DWDM systems rely upon accurate characterization of the EDFAs. However, nonlinearities and inhomogeneities in the EDFAs place stringent demands on the optical stimulus signals and measurements used to characterize the EDFAs. For example, to accommodate for effects such as polarization hole burning (PHB) when characterizing gain of an EDFA, measurements are performed and then averaged as the polarization states of the simultaneously applied optical stimulus signals at each wavelength are randomly varied. To assure that both the relative and absolute polarization states of the optical stimulus signals are sufficiently randomized, each optical signal is applied to a separate polarization scrambler. The randomized optical signals are then combined and applied to the EDFA. While this scheme provides optical stimulus signals well suited for characterizing EDFAs, it involves multiple polarization scramblers, one for each of the simultaneously applied optical signals, thereby increasing the cost and complexity of characterizing EDFAs.
To reduce the cost and complexity of providing optical stimulus signals, alternate schemes first combine the multiple optical signals at the different wavelengths and then time-vary the polarization states of the combined signals using a single polarization scrambler. While these schemes randomly vary the absolute polarization states of the multiple optical signals, unless random variations in the relative polarization states of the optical signals are also introduced, the polarization states of the optical stimulus signals remain correlated and the signals are insufficiently randomized to accommodate for PHB when used to characterize EDFAs. Accordingly, there is a need for a scrambling device that has low cost and complexity and that randomizes relative and absolute polarization states of simultaneously applied optical signals having different wavelengths.